Components of exhaust systems are, for example, mufflers, particle filters, catalytic converters. Complex exhaust gas treatment device, which combine a plurality of functions at the same time and may contain, for example, a particle filter, various catalytic converters and a muffler, are known as well. In addition to an SCR catalytic converter, there exists in SCR systems a reducing agent introduction means, by means of which a usually liquid reducing agent can be introduced into an exhaust gas stream upstream of the SCR catalytic converter. To make it possible to mix the reducing agent sufficiently with the exhaust gas, a mixing tube, which defines a mixing section and/or which may contain a static mixer, is usually arranged between the reducing agent introduction device and the SCR catalytic converter. SCR device “Selective Catalytic Reduction.” An aqueous urea solution may usually be used as a reducing agent.
A first part is usually inserted into a second part in a plurality of such exhaust system components. For example, a tube acting as a first part of the component may be passed through a bottom as a second part of the component in such a component. The respective bottom may have a passage opening for this, which is enclosed by a conduit. This conduit is advantageously formed integrally with the respective bottom. For example, such a conduit may be manufactured as a so-called “eyelet,” i.e., by deformation. This conduit defines an outer jacket section of the second part. A section of the tube arranged in the conduit defines here an inner jacket section of the first part. To fix the tube to the bottom, it is common to prepare a plurality of welding spots distributed in the circumferential direction or to prepare a closed, circumferential weld seam. To make it possible to insert the tube into the passage opening in a simple manner, a radial clearance is usually provided between an outer contour of the tube and an inner contour of the conduit. In case only weld spots arranged in a distributed pattern are used instead of a circumferential weld seam, the radial clearance may be dimensioned such that sufficient sealing can be achieved between the bottom and the tube. The sealing action is achieved here in the manner of a choke sealing gap. Avoidance of excessive leaks is in the foreground here, whereas an especially good sealing action is not necessary, as a rule. To achieve the desired sealing action, it is necessary for the radial clearance to be distributed as uniformly as possible in the circumferential direction. If more stringent requirements are imposed on the tightness of the connection, it is, however, preferable to prepare a closed, circumferential weld seam. It was found that the radial clearance is usually smallest during conventional assembly in the area of the first weld spot or of the beginning of the weld seam, whereas it is usually the greatest diametrically opposite the first weld spot or the beginning of the weld seam. Expensive finishing operations may become necessary as a result.
A corresponding problem also arises when inserting a static mixer as the first part into an exhaust pipe, as a further part, if a jacket of the mixer is to be fixed in the exhaust pipe by means of weld joints.